In recent months, the rate has fallen not so much because of robust hiring but because many people without a job have stopped looking for one, she and other economists say. Once people stop looking for a job, they’re no longer counted as unemployed, and the rate can fall as a result.

Yellen said that the U.S. economy is “not close to full employment,” even as the unemployment rate has dropped a full percentage point over the past 12 months.

With stimulus no longer tied to the unemployment rate, Yellen tried at her first news conference as Federal Reserve chair on Wednesday to clarify a question that’s consumed investors: When will the Fed start raising short-term interest rates from record lows?

Yellen said the Fed intends to keep short-term rates near zero for a “considerable” time and would raise them only gradually.

She said the Fed wouldn’t be dictated solely by the unemployment rate, which she feels no longer fully captures the job market’s health. She listed other employment measures the Fed also will track:

The U-6

It might sound like the name of an Irish rock band. But it’s a broader measure of the job market. It includes not only the unemployed but also those working part time who would prefer full-time work and those who have stopped searching for jobs. Last month, the U-6 rate was 12.6 percent, much higher than the unemployment rate of 6.7 percent. Yellen said the number of Americans forced to work part time is “unusually large.” It suggests that she believes the Fed could do more to boost the economy.

Long-term unemployed

One particularly brutal aspect of the Great Recession and its aftermath is that millions of laid-off people have struggled to find jobs. In April 2010, 45 percent of the unemployed had been out of work for six months or longer, a record. This proportion has since declined to 37 percent. But that’s still far higher than the pre-recession figure of just 17 percent. Yellen said it “has been immensely high and can be very stubborn” to bring down.

Labor force participation rate

This measure is critical to evaluating the job market’s health. It tracks how many people are either working or looking for work. In December, it fell to its lowest level in 35 years before recovering slightly. Retirements by baby boomers account for some of the drop. But Yellen said this rate has also fallen because some of the unemployed have given up looking for work. They could start searching again as the economy improves. If so, they could push up the unemployment rate.

Quitting and hiring

In a healthy economy, more Americans quit their jobs. That’s because they either have a new job — usually with higher pay — or they’re confident they can find another. That makes quitting a reliable measure of the job market’s health. Yellen wants to see whether employers are actively adding workers. The number of people quitting jobs has partly recovered from the recession. But Yellen noted that hiring “remains extremely depressed.”

Wage growth

Yellen highlighted what everyone who has gone without a decent raise for several years knows: “Wage growth has really been very low.” Average pay is rising at a 2 percent annual pace, before inflation, well below the 3 percent to 4 percent rate she cited as typical of a healthy economy, she said.

Yellen’s assessment wasn’t all gloomy.

The “dial on virtually all of those things is moving in a direction of improvement,” she said.